1. Field of the Invention
The present invention relates to a polymer with at least one pericyclic protective group, and more particularly to a resist composition containing the polymer.
2. Description of the Prior Art
Nowadays, thin film coating technique plays a very important role in chemical engineering technology. A resin suitable for thin film coating should meet the requirements of having good film properties and good adherence to substrates. Therefore, the glass transition temperature of such resin should not be too high. To be considered for application to IC photoresists (resists), a suitable resin should further have other properties such as high etch and heat resistance, properties which are frequently achieved by molecular design.
With increasing integration of semiconductor devices, there is a heightened need to form finer patterns in photolithography processes. A photolithography technology has been proposed which utilizes an ArF excimer laser as a source to generate radiation having a wavelength of 193 nm for producing devices beyond the 1 giga capacity. This technology is intended to replace conventional KrF excimer laser which generates radiation having a wavelength of 248 nm.
A chemically amplified resist composition is a well-known resist composition that is suitable for use in the 193 nm photolithography. The photoresist solution includes a protected resin, a photoacid generator, and a solvent. The so-called protected resin is a resin that is protected by an acid-labile protective group. The resin will be converted into alkali-soluble when the acid-labile protective group is decomposed. When a positive chemically amplified resist composition applied on a substrate is exposed to light, the photoacid generator will generate acid, and the acid will decompose the acid-labile protective group in the resin, thus making the resinsoluble in an alkali developer.
Ito et al. in U.S. Pat. No. 4,491,628 discloses a resist composition in which the resin is protected by t-butyl esters of carboxylic acid. The examples of such protected resins include poly(tert-butyl p-vinylbenzoate) and poly(tert-butyl methacrylate). However, such a resist composition has an insufficient etch resistance and resolution. Moreover, post exposure baking (PEB) should be conducted at a high temperature, so that the integrated circuits are easily degraded, and problems such as proximity effect (isoline and denseline bias) and edge roughness are thus induced.
Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a novel polymer that exhibits strong etch resistance.
Another object of the present invention is to provide a novel polymer that has the required properties for use in chemically amplified resist for use with ArF laser.
A further object of the present invention is to provide a photoresist composition comprising the novel polymer, which can be post exposure baked at a lower temperature. Thus, problems of the proximity and edge roughness can be solved.
To achieve the above objects, the present invention provides a polymer containing at least one pericyclic protective group G having a formula selected from the group consisting of: 
wherein
R1 is selected from the group consisting of linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, and 
R2, R3, R4, and R5 can be the same or different and are independently selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, and 
wherein R11 is selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, arid R12 is an alkylene group having from 1 to 10 carbon atoms;
X1 and X2 can be the same or different and are independently selected from the group consisting of a halogen, hydroxy, C1-15 alkoxy, NH2, NHR61, NR61R62, SH, SR63, xe2x80x94(Cxe2x95x90O)H, xe2x80x94(Cxe2x95x90O)OH, xe2x80x94(Oxe2x95x90O)R64, xe2x80x94(Cxe2x95x90O)OR65, each of R61, R62, R63, R64, and R65 being linear or branched alkyl having from 1 to 10 carbon atoms or cyclic alkyl having from 3 to 15 carbon atoms;
n, which denotes the degree of substitution of the ring to which X1 is attached, is from 0 to 5;
m, which denotes the degree of substitution of the ring to which X2 is attached, is from 0 to 5;
a is from 1 to 5; and
in formula (III), when one of R2 and R3 is hydrogen, R2 and R3 are different.
A first aspect of the present invention is that it provides a novel polymer containing at least one pericyclic protective group G selected from formulae (I) to (V). That is to say, the polymer may contain only one group G, two groups G, three groups C, four groups G, or even five groups G. The combination of the groups G is not limited.
In formulae (I) to (V), R1 is selected from the group consisting of linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, and 
R2, R3, R4, and R5 can be the same or different and are independently selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, and 
wherein R11 is selected from the group consisting of hydrogen, linear or branched alkyl, alkenyl, alkylaryl, arylalkyl having from 1 to 10 carbon atoms, cyclic alkyl having from 3 to 15 carbon atoms, alkoxyl having from 1 to 10 carbon atoms, and R12 is an alkylene group having from 1 to 10 carbon atoms.
Representative examples of R1, R2, R3, R4, and R5 include hydrogen, methyl, ethyl, propyl, butyl, isobutyl, amyl, isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, vinyl, allyl, phenyl, and tosyl. But R1 can not be hydrogen.
X1 and X2 can be the same or different and are independently selected from the group consisting of halogen, hydroxy, C1-15 alkoxy, NH2, NHR61, NR61R62, SH, SR63, xe2x80x94(Cxe2x95x90O)H, xe2x80x94(Cxe2x95x90O) OH, xe2x80x94(Cxe2x95x90O)R64, xe2x80x94(C=O)OR65 each of R61, R62, R63, R64, and R65 being linear or branched alkyl having from 1 to 10 carbon atoms or cyclic alkyl having from 3 to 15 carbon atoms.
Representative examples of X1 and X2 include fluorine, chlorine, hydroxy, methoxy, ethoxy, xe2x80x94NH2, xe2x80x94N(CH3)2, xe2x80x94SH, xe2x80x94SCH3, xe2x80x94(Cxe2x95x90O)H, xe2x80x94(Cxe2x95x90O)OH, xe2x80x94(CO)CH3, xe2x80x94(Cxe2x95x90O) OCH3, and xe2x80x94(Cxe2x95x90O)OC(CH3)3 (t-butyloxycarbonyl).
When the polymer of the present invention contains a pericyclic protective group of formula (I) and n is 1, then preferably X1 is t-butyloxycarbonyl, and R1 is alkyl having from 1 to 10 carbon atoms, preferably methyl.
When the polymer of the present invention contains a pericyclic protective group of formula (I) and n is 0, then preferably R1 is alkyl having from 1 to 10 carbon atoms, preferably methyl.
When the polymer of the present invention contains a pericyclic protective group of formula (I) and n is 3, then preferably two X1 are halogen groups, and one X1 is OH.
According to the present invention, the polymer can be a homopolymer or a copolymer containing at least one pericyclic protective group G as defined above. When the polymer of the present invention is a copolymer, one example can be a block or random copolymer having the repeating units (VI), (VII), (VIII), (IX), and (X): 
wherein
R71, R72, and R76 can be the same or different and are independently hydrogen, linear or branched alkyl having from 1 to 10 carbon atoms or cyclic alkyl having from 3 to 15 carbon atoms, provided that at least one of R71, R72, and R76 is a pericyclic protective group G;
R73, R74, R75, and R77are the same or different and are independently hydrogen, linear or branched alkyl having from 1 to 10 carbon atoms or cyclic alkyl having from 3 to 15 carbon atoms; and
the molar ratios of the repeating units (VI), (VII), (VIII), (IX) and (X) are w, x, y, z, and s respectively, wherein w+x+y+z+s=1, 0.8xe2x89xa7wxe2x89xa70, 0.5xe2x89xa7xxe2x89xa70, 0.8xe2x89xa7yxe2x89xa70.1, 0.5xe2x89xa7z greater than 0, 0.2xe2x89xa7sxe2x89xa70.
When z and w are larger than 0, at least one of R71, R72, and R76 is a pericyclic protective group G. When z and w are both equal to 0, R72 is a pericyclic protective group G. When z=0 and w greater than 0, at least one of R71 and R72 is a pericyclic protective group G. When w=0 and z greater than 0, at least one of R72 and R76 is a pericyclic protective group G.
When z=0 and w greater than 0, at least one of R71 and R72 is a pericyclic protective group G as defined above, and the other is preferably an acid-labile protective group. Similarly, when w=0 and z greater than 0, at least one of R72 and R76 is a pericyclic protective group G as defined above, and the other is preferably an acid-labile protective group. Thus, such a polymer can be used as a chemically amplified resist. The acid-labile protective group will be decomposed in the presence of an acid, so as to make the polymer alkali-soluble.
When z and w are both larger than 0, among R71, R72, and R76, at least one is a pericyclic protective group G as defined above and the other one or the other two are preferably acid-labile protective groups. Thus, such a polymer can be used as a chemically amplified resist.
When w, x and z are larger than 0 and s is equal to 0, an example of such a copolymer is that R71 is tert-butyl, R73 is hydrogen, R74 and R75 are methyl, R74 and R76 are pericyclic protective groups represented by formula (I). Preferably, R72 and R76 are 2-methyl-2-bicyclo[2,2,1]heptanyl.
To make the polymer of the present invention suitable for thin film coating, the polymer is preferably soluble in an organic solvent. A preferable polymer of the present invention has a glass; transition temperature (Tg) higher khan 100xc2x0 C., preferably 130xc2x0 C. to 300xc2x0 C., a weight average molecular weight of 300 to 50000, and a decomposition temperature (Td) higher than 130xc2x0 C., preferably 160xc2x0 C.
A second aspect of the present invention is that it provides a resist composition containing at least one polymer of the present invention described above and a photoacid generator, wherein the photoacid generator is present in an amount of from 1 to 20% by weight of the polymer.
Any suitable photoacid generator may be used. Preferred photoacid generators include, but are not limited to, triarylsulfonium salts, diaryliodonium salts, sulfonates, and mixtures thereof. Representative examples of the triarylsulfonium salts include triphenyltriflate, triphenylantimonate, methoxytriphenyltriflate, methoxytriphenylantimonate, trimethyltriphenyltriflate, and naphthalenetriflate. Representative examples of the diaryliodonium salts include diphenyliodoniumtriflate, di-t-butylbisphenyl-antimonate, and di-t-butylbisphenyltriflate.
The resist composition of the present invention is photosensitive at a wavelength of 150 nm to 650 nm, preferably at a wavelength of 193 nm or 248 nm.